Silicon-germanium (SiGe) has been proven to be an effective material to improve performance of transistor devices. For example, SiGe material can be used for source and drain (S/D) regions of a PMOS device to improve device carrier mobility by exerting compressive stress in the channel region.
Ultra-high temperature (UHT) millisecond anneal has also been applied to transistor devices with a view to maximizing electrical activation by increasing dopant solid solubility in semiconductor materials. For example, an UHT anneal can be performed to activate doped source/drain regions at a high temperature of more than 1150° C., while a conventional thermal anneal typically has a low peak temperature limited under 1100° C.
Problems arise, however, due to the low melting point of the SiGe material. For example, the melting point of a SiGe material that contains 20% Ge can be approximately 1275° C., which is lower than the melting point of the traditional material silicon as about 1414° C. In addition, the higher the Ge concentration, the lower the melting point of the SiGe material. Depending on the annealing temperature used, the SiGe material with low melting point may therefore be melted during the UHT anneal and subsequently re-crystallized while cooling down. This re-crystallization of the SiGe material can cause wafer warpage that generates permanent damage to the entire device in subsequent processes. For example, because of wafer warpage, lithographic pattern misalignment can be incurred during the subsequent contact patterning and/or dielectric patterning steps.
Thus, there is a need to overcome these and other problems of the prior art and to provide methods for implementing UHT anneal on SiGe semiconductor materials.